In recent years, the development of a measurement system including remote power meter reading has been forwarded in environment where the Internet is available.
There is used a power meter using a method in which a sensor that detects rotation is added, or an ammeter (CT) and a voltmeter (PT) are newly added to an existing integrating power meter that converts a used electric power into the number of rotations of a disc, and conducts integration operation, and multiplicative computation is conducted by an electric circuit or a microprocessor to measure the electric power. However, the power meter of this type is not only upsized in device, but also expensive, and would also consume an unnecessary energy.
Under the circumstances, there has been desired the development of the power meter which can measure a power consumption as the quality of electricity as it is, and can be also downsized and integrated.
In particular, there has been proposed a power measurement device that can measure the power consumption as the quantity of electricity as it is, by the aid of a magnetoresistive effect of a magnetic thin film (Non Patent Documents 1 and 2).
This power measurement device is configured so that a magnetic thin film that is put in parallel to a primary conductor into which AC current flows (configured on a substrate) is used, a primary voltage is applied to both ends of the magnetic thin film through a resistor, and an output is extracted from (both ends) of the magnetic thin film. The power measurement device is of a system in which an electric power IV is extracted from an amplitude value of a second harmonic component.
In the power measurement device, a signal component proportional to the electric power is extracted, paying attention to a fact that a linear characteristic can be obtained with no bias magnetic field by the aid of a planar hall effect that is a phenomenon in which a resistance value of a magnetic material is changed according to an angle formed between current and magnetization.
The magnetic field sensor used in this device is an element that converts a change in external magnetic field into an electric signal, which patterns a magnetic thin film such as a ferromagnetic thin film or a semiconductor thin film, and allows current to flow in a pattern of the magnetic thin film to convert the change in the external magnetic field into an electric signal as a voltage change.
In this example, an output signal is represented as the following Expression (1).
                                              ⁢                  (                      Math            .                                                  ⁢            1                    )                                                                                          V            mr                    =                                                                                                                                                                  R                          ⁢                                                                                                          ⁢                                                      1                            ·                            R                                                    ⁢                                                                                                          ⁢                          3                                                -                                                  R                          ⁢                                                                                                          ⁢                                                      2                            ·                            R                                                    ⁢                                                                                                          ⁢                          4                                                                                                                      R                          ⁢                                                                                                          ⁢                          1                                                +                                                  R                          ⁢                                                                                                          ⁢                          2                                                +                                                  R                          ⁢                                                                                                          ⁢                          3                                                +                                                  R                          ⁢                                                                                                          ⁢                          4                                                                                      ·                                          2                                                        ⁢                                      I                    2                                    ⁢                  cos                  ⁢                                                                          ⁢                  ω                  ⁢                                                                          ⁢                  t                                ω                                            ︷                                  (                                      A                    ⁢                                                                                  ⁢                    1                                    )                                                      +                                                                                                                                                                                                                                                                                    k                                  ·                                  R                                                                ⁢                                                                                                                                  ⁢                                3                                                                                                                              R                                  ⁢                                                                                                                                          ⁢                                  1                                                                +                                                                  R                                  ⁢                                                                                                                                          ⁢                                  2                                                                +                                                                  R                                  ⁢                                                                                                                                          ⁢                                  3                                                                +                                                                  R                                  ⁢                                                                                                                                          ⁢                                  4                                                                                                                      ·                                                          I                              1                                                        ·                                                          V                              1                                                                                ⁢                          cos                          ⁢                                                                                                          ⁢                          θ                                                                          D                          ⁢                                                                                                          ⁢                          C                                                                    +                                                                                                                                                                                                                                                                              k                                ·                                R                                                            ⁢                                                                                                                          ⁢                              3                                                                                                                      R                                ⁢                                                                                                                                  ⁢                                1                                                            +                                                              R                                ⁢                                                                                                                                  ⁢                                2                                                            +                                                              R                                ⁢                                                                                                                                  ⁢                                3                                                            +                                                              R                                ⁢                                                                                                                                  ⁢                                4                                                                                                              ·                                                      I                            1                                                    ·                                                      V                            1                                                                          ⁢                                                  cos                          ⁡                                                      (                                                                                          2                                ⁢                                ω                                ⁢                                                                                                                                  ⁢                                t                                                            +                              θ                                                        )                                                                                                                      2                        ⁢                        ω                                                                                                                        ︷                                  (                                      A                    ⁢                                                                                  ⁢                    2                                    )                                                      +                          harmonic              ⁢                                                          ⁢              component                                      ⁢                                  ⁢                                  ⁢                  P          =                                    I              ·              V              ·              cos                        ⁢                                                  ⁢            θ                                              (        1        )            
In this expression, the output is divided into a term of a DC component and a term of an AC component.
A1 is an unnecessary term irrelevant to an electric power developed by unbalance of bridge resistors, and A2 is a term (instantaneous electric power) proportional to the electric power.
A variety of proposals have been made to enhance the sensitivity of the magnetic field sensor. For example, Patent Document 1 has also proposed a magnetic field sensor in which a part of an annular pattern is opened to form a current carrying part for designing the high sensitivity.